A Vuilleumier heat pump (VHP) is a thermodynamic apparatus in which thermal energy from a source, such as a combustor, as well as energy from the environment is extracted to provide heating. The amount of energy available for heating is greater than the amount of fuel energy supplied to the combustor because it is supplemented by the energy from the environment.
VHPs have been built with a crank system that couples two displacers, an example VHP 10 is shown in FIG. 1. A crank 16 is used to start the reciprocation of the hot displacer 12 and the cold displacer 14. Displacers 12 and 14 reciprocate in a cylinder 26 that is within a housing 18. Displacer 12 and 14 separate the volume within cylinder 26 into three volumes: a hot volume 20, a warm volume 22, and a cold volume 24. The mass of the crank 16, optionally with a flywheel maintains the displacer reciprocation, even when forces acting upon the displacers 12 and 14 might otherwise cause the displacers to fail to reciprocate to its end of travel.
In a system disclosed in commonly-assigned patent application U.S. 2015/0075209, displacers are caused to move between ends of travel by a spring acting on the displacer as shown in FIG. 2. A heat pump 250 has a housing 252. A cylinder 254 is provided in housing 252. A hot displacer 262, which can reciprocate within cylinder 254 is at its lowest point of travel. A cold displacer 266, which can also reciprocate within cylinder 254 is at its high point of travel. The displacers define three chambers: a hot chamber 272, a warm chamber, and a cold chamber 276. With the positions of displacers 262 and 266 as illustrated in FIG. 2, the warm chamber has no volume and is thus not provided a numeral. Housing 252 has a hot end 282 and a cold end 286. Energy is provided by an energy source 290 to the hot end of heat pump 250. Energy source may be a burner and may be supplemented by solar energy.
A post 288 is affixed to the cold end 286 of housing 252 and extends into housing 252 along a central axis of housing 252. Post 288 extends through cold displacer 266 and extends into one end of hot displacer 262. Post 288 has electromagnets 292a and 292c disposed within hot displacer 262 and electromagnets 296a and 296c disposed within cold displacer 266.
Ferromagnetic elements or blocks 222a, 222b, and 222c are affixed to hot displacer 262. Blocks 222a, 222b, and 222c are displaced from each other by predetermined distances as measured in a direction along the axis of housing 252. The predetermined distances are related to the desired travel of hot displacer 262. Ferromagnetic blocks 226a, 226b, and 226c are affixed to cold displacer 266. Blocks 226a, 226b, and 226c are displaced from each other by predetermined distances as measured in a direction along the axis of housing 252.
It has been found that coil 292a that is the closest to energy source 290 becomes too hot to operate properly. Thus, the mechatronics driving system should be moved to a cooler portion of heat pump 250.
In DE 4206958 A1, mechatronics 60 of a Vuilleumier heat pump 50 is disposed in the cold end of the heat pump. Heat pump 50 has a cylinder 52 in which a hot displacer 54 and a cold displacer 56 reciprocate. Heat pump 50 has a burner 58 or other suitable energy source. Hot displacer 54 is coupled to a ferromagnetic arm 84 that is disposed between two coils 80 and 82. Coils 80 and 82 are surrounded by spring 86 and 88, respectively. Hot displacer 54 is in its upward end of travel as shown by spring 86 being substantially fully compressed. Coil 80 is holding ferromagnetic arm 84 at the position shown. When, coil 80 is commanded to release arm 84, hot displacer 54 and arm 84 will move downward from the force of spring 86. At such time spring 88 would become compressed and to hold hot displacer in its downward end of travel, coil 82 would be commanded to exert first a grabbing attractive force and after arm 84 is proximate coil 82, a holding force.
Cold displacer 56 is shown at its lower end of travel in FIG. 3. A ferromagnetic arm 74 is coupled to cold displacer 54 and transmits forces acting on arm 74 to cold displacer 56. A coil 76 is above arm 74. Coil 76 can be commanded to attract arm 74. Spring 76 and 78 act upon arm 74 to cause cold displacer 56 to move from one end of travel to the other end of travel. However, due to losses in the system and other forces acting upon cold displacer 56, cold displacer 56 can fail to reach the end of travel (or in other undesirable instances, hits when it gets to the other end of travel). The appropriate one of coils 70 and 72 is energized to attract ferromagnetic arm 74 to grab and then hold arm 74. As arm 74 is coupled to cold displacer 56, such action holds cold displacer 56 in place.
The configuration in FIG. 3 is chosen because it minimizes that length taken up by the mechatronics 60. However, because everything is off-center, some cocking can occur. Furthermore, assembling items that are off-center can present challenges to maintain desired assembly accuracy.